Known gas generators generally include permeation-tube calibrators and electrolytic calibrators. Calibrators are typically used to calibrate monitors for determining the safe or unsafe conditions of a potentially hazardous gaseous environment, but may also be used to calibrate instruments for determining a concentration of any gaseous stream. For obvious reasons, reliability and accuracy of calibrating these monitors and instruments are generally very important functions.
Permeation-tube calibrators typically utilize a sealed tube containing the gaseous material of interest. The tube is sealed with a membrane and the gas in the tube is usually maintained in a liquid state. Because the membrane may be permeable to a wide range of substances, molecules of the contained gas may dissolve and diffuse through the membrane into the surrounding atmosphere. Although precise and accurate concentrations of specific gases may be generated by this method, disadvantages of permeation-tube calibrators include a non-adjustable gas concentration, limited portability, and limited useful life. A further disadvantage is that gas is constantly being generated and may present a toxic hazard. A further disadvantage of permeation-tube calibrators includes temperature sensitivity, whereby changing temperatures may negatively affect accuracy of gas generation and response time.
Electrolytic calibrators typically generate pure gas by passing an electric current through a reagent electrolyte solution. The gas generated escapes as bubbles from the solution and is dispersed in a gas stream to form a gas mixture of known concentration. The size or quantity of bubbles produced, however, are often difficult to control and may undesirably lead to a lack of stability and sensitivity of the electrolytic calibrator.
U.S. Pat. No. 4,460,448 to Wolcott (“Wolcott”) relates to an invention for producing mixtures of known concentrations of oxidizing or reducing gases. Wolcott provides an electrochemical cell having a first electrode, an oxidizing or reducing gas generating electrode, an electrolyte providing the ions that make up the oxidizing or reducing gases, and a membrane in between and in contact with the electrolyte and gas generating electrode for controlling the flow of electrolyte and filtering desirable ions to the gas generating electrode. The electrochemical cell further includes a porous membrane in contact with the gas generating electrode for minimizing the thickness of electrolyte solution around the gas generating electrode and, secondarily, for regulating the flow of gas released from the electrode.
U.S. Pat. No. 5,395,501 to Rohrbacker et al. (“Rohrbacker”) relates to an electrochemical cell having a gas generator. The gas generator includes a first electrode, a gas generating electrode, an electrolyte fluid, and a membrane that is permeable to gas for permitting gas to diffuse through it but impermeable to the electrolyte for preventing a loss of fluid. The gas generator provides membranes on several sides of the generator such that, in any orientation, undesirable bubbles that form from the gas generating electrode may vent.
A disadvantage of both Wolcott and Rohrbacker is that they require a membrane for controlling or regulating the bubbles produced from the gas generating electrode. Diffusing gas through a membrane increases the time to generate gas and undesirably affects a gas generator's efficiency. In addition, both Wolcott and Rohrbacker use another membrane for electrolyte to pass through before reaching the gas generating electrode. This also increases the time for the gas generator to respond and further decreases efficiency. Moreover, the references disclose electrochemical gas generators having numerous components in order to function properly, thereby increasing cost.
What is desired, therefore, is to provide an electrochemical gas generator where the gas being generated may be regulated. What is also desired is to provide a gas generator that minimizes the formation of bubbles. What is further desired is an efficient gas generator having improved response time and temperature stability.